1. Field of the Invention
The present invention relates to a vector control system for a permanent magnet synchronous motor.
2. Description of the Prior Art
In a motor constant identification technology, as described in Japanese Patent Laid-open No. 2001-145399, which is used in a vector control system applied to a permanent magnet synchronous motor, the values of d-axis and q-axis voltages detected by a voltage detector attached to a power converter are used in calculation for identifying motor constants in three processes described below.
(1) An induced voltage coefficient of the motor is identified from a difference in the q-axis (torque) component in vector control between a voltage command value and a detected voltage.
(2) A motor resistance is identified from a difference in the d-axis (magnetic flux) component between a voltage command value and a detected voltage.
(3) If the resistance identified in (2) above exceeds a limit value, a switchover is made to an operation in which a q-axis inductance is identified from the voltage difference in the d-axis component.